Chirped-pulse Regenerative Amplifier Research Articles

Milli-joule class femtosecond regenerative amplifier enabled by a narrowband fiber oscillator

We report on a room-temperature operated, Yb:CaF2 based, chirped-pulse regenerative amplifier system with a pulse duration of 300 fs and an output pulse energy of 2.0 mJ. A novel front end comprising a narrowband fiber oscillator and a nonlinear fiber amplifier is adopted to seed the regenerative amplifier. To achieve broadband spectral coverage for femtosecond pulse generation, nonlinear fiber amplification is implemented and spurs a 7-folded spectral extension. After the successive pulse stretching, spectral reshaping, regenerative amplifying, and compressing, optimum pulses with 300-fs duration and 6.7-GW peak power are obtained. Such intense pulses are capable of inducing laser filament at 0.4-mJ energy with a loosely focusing geometry. Our method demonstrates the potential of narrowband fiber lasers to enable femtosecond regenerative amplifiers and paves the way toward compact, robust, and cost-effective millijoule-class lasers.

Numerical and Experimental Analysis of Yb:YAG Thin Disk Regenerative Amplifier

We present an numerical and experimental analysis of a Yb:YAG thin disk regenerative amplifier. Group velocity dispersion, third order dispersion, and self-phase modulation (SPM) effects are considered in the simulations of the amplification process. By virtue of the simulations, a compact femtosecond Yb:YAG thin-disk chirped-pulse regenerative amplifier delivering an average power of 50 W at a central wavelength of 1030 nm with a propagation factor of M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <; 1.4 at a repetition rate of 200 kHz and a pulse duration of 500 fs was constructed. Numerical simulation based on this Yb:YAG thin-disk was carried out to investigate the pulse parameters evolution in each round trip. The measured experimental results in pulse width, spectrum, and pulse energy together fitted quite well with the numerical simulation. This plays an important role in the design of high-peak-power regenerative amplifier and will facilitate further power scaling and suppression of gain narrowing of the whole system.

Compact millijoule Yb3+:CaF2 laser with 162 fs pulses.

We report on a compact diode-pumped, chirped pulse regenerative amplifier system with a pulse duration of 162 fs and an output pulse energy of 1 mJ before as well as 910 µJ after compression optimized for the probing of ultrafast relativistic laser-plasma processes. A chirped volume Bragg grating (CVBG) acts as a combined pulse stretcher/compressor representing a robust solution for a CPA laser system in the millijoule range. Yb3+:CaF2 is used as gain medium to support a large bandwidth of 16 nm (FWHM) when spectral gain shaping is applied. Chirped mirrors compensate for any additional dispersion introduced to the system.

Dual Wavelength Chirped Pulse Regenerative Amplifier Based on Yb&lt;sup&gt;3+&lt;/sup&gt;:LuAlO&lt;sub&gt;3&lt;/sub&gt; Crystal for Terahertz Applications

Compact diode-pumped chirped pulse regenerative amplifier systems with pulse repetition rate of hundreds kilohertz based on Yb 3+ -doped crystals are of practical importance for wide range of applications such as materials processing, medicine, scientific research, etc. The aim of this work was to study the Yb 3+ :LuAlO crystal based dual wavelength chirped pulse regenerative amplifier. Perovskite-like aluminate crystals have unique spectroscopic properties that allowed to use amplifier active element gain spectrum as an amplitude filter for amplified pulse spectrum and even obtained dual wavelength amplification without any additional components. In our work a simple way to obtain dual-wavelength operation of chirped pulse regenerative amplifier by using the active medium gain spectrum as an amplitude filter for the formation of the amplified pulses spectrum demonstrated for the first time to our knowledge. Maximum output power of 5.4 W of chirped pulses (3.8 W after compression) and optical-to-optical efficiency of 22.5 % have been obtained for Yb:LuAP E//b-polarization at 200 kHz repetition rate. Compressed amplified pulse duration was about 708 fs while separate spectral components durations were 643 fs and 536 fs at 1018.3 nm and 1041.1 nm central wavelengths, respectively. Performed investigations show high potential of Yb 3+ :LuAP crystals as active elements of compact diode pumped chirped pulse regenerative amplifiers

Numerical investigation on the spectral and temporal characteristics of amplified spontaneous emission in chirped pulse regenerative amplifiers

Accurate characterization of the amplified spontaneous emission (ASE) is greatly important for designing a high-contrast chirped pulse amplifier (CPA). In this paper, we develop a theoretical model based on small signal gain calculation (SSGC) to simulate the temporal and spectral profiles of the ASE output power of a chirped pulse regenerative amplifier. Also, the finite difference time domain (FDTD) is utilized as a robust mathematical method to describe ASE characteristics. Comparison of the two methods introduces the developed SSGC as a fast, greatly efficient and accurate technique to predict and analyze the ASE behavior in a CPA system.

Femtosecond Laser Filaments for Use in Sub-Diffraction-Limited Imaging and Remote Sensing.

Probing remote matter with laser light is a ubiquitous technique used in circumstances as diverse as laser-induced breakdown spectroscopy and barcode scanners. In classical optics, the intensity that can be brought to bear on a remote target is limited by the spot size of the laser at the distance of the target. This spot size has a lower bound determined by the diffraction limit of classical optics. However, amplified femtosecond laser pulses generate intensity sufficient to modify the refractive index of the ambient air and undergo self-focusing. This self-focusing effect leads to the generation of highly intense laser filaments which maintain their intensity and small sub-millimeter diameter size at distances well beyond the classical Rayleigh length. Such intensity provides the capability of remote scanning, imaging, sensing, and spectroscopy with enhanced spatial resolution. We describe a technique for generating filaments with a femtosecond regenerative chirped-pulse amplifier, and for using the resulting filament to conduct imaging and spectroscopic measurements at remote distances of at least several meters.

Growth, spectroscopy and high power laser operation of Yb:YAl3(BO3)4 crystal: Continuous-wave, mode-locking and chirped pulse regenerative amplification

We report on growth, spectroscopy and continuous-wave, mode-locking lasing and chirped pulse regenerative amplification of Yb:YAl3(BO3)4 (Yb:YAB) crystal. Efficient CW laser operation with 9.2 W output power, 46% optical-to-optical and 74% slope efficiencies was demonstrated. Efficient SESAM mode-locked Yb:YAB bulk laser was demonstrated for σ-polarization with 4 W average output power at 70 MHz pulse repetition frequency (PRF) and 195-fs pulse duration resulting in the pulse energy of 57 nJ and pulse peak power of 0.3 MW. Optical-to-optical efficiency of 27% in mode-locked regime is demonstrated. Chirped pulse regenerative amplifier based on Yb:YAB crystal demonstrated with maximum output power of 4.6 W (6 W of chirped pulses and optical-to-optical efficiency of 25%) and 695 fs pulse duration at 100 kHz PRF for the first time to the best of our knowledge.

Yb:CALYO-based femtosecond chirped pulse regenerative amplifier for temporally resolved pump-probe spectroscopy

Diode-pumped femtosecond chirped pulse regenerative amplifiers based on Yb3+-materials are of practical importance for wide range of scientific, industrial and biomedical applications. The aim of this work was to study the amplification of broadband chirped femtosecond pulses in regenerative amplifier based on Yb3+:CaYAlO4crystal.Such systems use femtosecond mode-locked lasers as seed pulse sources and amplify nJ-seed pulses to sub-mJ energy range. Most chirped pulse regenerative amplifier systems described in the literature use seed lasers with typical pulse spectral width at the level of 10–15 nm full width at half maximum (FWHM) that limit the seed pulse duration of about 90 fs and amplified pulse duration at the level of 200 fs due to strong influence of gain narrowing effect on the amplified pulse parameters. Yb3+-doped crystals with wide and smooth gain bandwidth as an active medium of chirped femtosecond pulse regenerative amplification systems allow to reduce negative contribution of gain narrowing effect and lead to shortening of amplified pulses. In this research we study the chirped pulse regenerative amplification of broad-band femtosecond pulses (60 nm spectral width FWHM) in the Yb3+:CaYAlO -based chirped pulse regenerative amplifier. Substantial reduction of the amplified pulse duration down to 120 fs (19.4 nm spectral width FWHM) with average power of 3 W at 200 kHz pulse repetition frequency was demonstrated without any gain narrowing compensation technique.The results of experimental investigation of broad-band seeded Yb3+:CaYAlO -based chirped pulse regenerative amplifier are reported for the first time to our knowledge. 120 fs-pulses (19.4 nm FWHM) with average output power of 3 W were demonstrated without any gain narrowing compensation technique. Despite the significant reduction of amplified pulse duration the task of improvement group velocity dispersion balance (including high orders of group velocity dispersion) remains relevant.

20 mJ, 1 ps Yb:YAG Thin-disk Regenerative Amplifier

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with turn-key performance and microjoule-level pulse energy is used to seed the regenerative chirped-pulse amplifier. The amplifier is placed in airtight housing. It operates at room temperature and exhibits stable operation at a 5 kHz repetition rate, with a pulse-to-pulse stability less than 1%. By employing a 1.5 mm-thick beta barium borate crystal, the frequency of the laser output is doubled to 515 nm, with an average power of 70 W, which corresponds to an optical-to-optical efficiency of 70%. This superior performance makes the system an attractive pump source for optical parametric chirped-pulse amplifiers in the near-infrared and mid-infrared spectral range. Combining the turn-key performance and the superior stability of the regenerative amplifier, the system facilitates the generation of a broadband, CEP-stable seed. Providing the seed and pump of the optical parametric chirped-pulse amplification (OPCPA) from one laser source eliminates the demand of active temporal synchronization between these pulses. This work presents a detailed guide to set up and operate a Yb:YAG thin-disk regenerative amplifier, based on chirped-pulse amplification (CPA), as a pump source for an optical parametric chirped-pulse amplifier.

20 mJ, 1 ps Yb:YAG Thin-disk Regenerative Amplifier.

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with turn-key performance and microjoule-level pulse energy is used to seed the regenerative chirped-pulse amplifier. The amplifier is placed in airtight housing. It operates at room temperature and exhibits stable operation at a 5 kHz repetition rate, with a pulse-to-pulse stability less than 1%. By employing a 1.5 mm-thick beta barium borate crystal, the frequency of the laser output is doubled to 515 nm, with an average power of 70 W, which corresponds to an optical-to-optical efficiency of 70%. This superior performance makes the system an attractive pump source for optical parametric chirped-pulse amplifiers in the near-infrared and mid-infrared spectral range. Combining the turn-key performance and the superior stability of the regenerative amplifier, the system facilitates the generation of a broadband, CEP-stable seed. Providing the seed and pump of the optical parametric chirped-pulse amplification (OPCPA) from one laser source eliminates the demand of active temporal synchronization between these pulses. This work presents a detailed guide to set up and operate a Yb:YAG thin-disk regenerative amplifier, based on chirped-pulse amplification (CPA), as a pump source for an optical parametric chirped-pulse amplifier.

Yb3+:LuAlO3 crystal as a gain medium for efficient broadband chirped pulse regenerative amplification.

The experimental study results of a chirped pulse amplification regime are reported for the Yb:LuAlO3 crystal with different polarization states in the gain media for the first time, to the best of our knowledge. Maximum output power of 5W with 565fs pulse duration was obtained for E//b-polarization at a 200kHz repetition rate seeded by a 98fs Yb:KYW oscillator. 165fs pulses with output power of 4.5W were demonstrated for E//c-polarized light in the crystal.

200 kHz 5.5 W Yb(3+): YVO4-based chirped-pulse regenerative amplifier.

A chirped-pulse regenerative amplifier based on a Yb:YVO4 (Yb:YVO) crystal was demonstrated for the first time, to our knowledge. A novel wavelength-independent off-axis technique was used to deliver 26.6 W of pump power with a low quantum defect. It was seeded by means of a 120 fs Yb:YVO4 oscillator. It generates as much as 5.5 W of average output power with chirped pulses and 4.2 W with 200 fs compressed pulses at a 200 kHz repetition rate. A maximum pulse energy of 140 μJ was obtained at pulse repetition frequencies up to 25 kHz at the central wavelength of 1018 nm.

Single-grating-mirror intracavity stretcher design for chirped pulse regenerative amplification.

We report for the first time, to the best of our knowledge, an innovative design concept for intracavity pulse stretching in a regenerative amplifier, employing a single "grating-mirror" based on a leaky-mode grating-waveguide design. The very compact and flexible layout allows for femtosecond pulses to be in principle easily stretched up to nanosecond durations. The design has been tested in a diode-pumped Yb:CALGO regenerative amplifier followed by a standard transmission grating compressor. Sub-200-fs pulses (stretched pulses ≈110 ps) with 205-μJ energy at 20-kHz repetition rate have been demonstrated. In order to prove the robustness and potential for energy scaling of leaky-mode grating-waveguide intracavity stretcher, we generated stretched pulses with energies of up to ≈700 μJ (400-ps long) at a lower repetition rate of 10kHz. A simple model is proposed for the study of the cavity in presence of induced spatial chirp.

Broadening and Amplification of an Infrared Femtosecond Pulse for Optical Parametric Chirped-Pulse Amplification

A high-average-power diode-pumped narrowband regenerative chirped pulse amplifier is developed using the thin-rod Nd:YAG laser architecture for optical parametric chirped-pulse amplification (OPCPA). The effect of the etalons on the amplified pulse in the regenerative cavity is studied experimentally and theoretically. By inserting glass etalons of thickness 1 mm and 5 mm into the regenerative cavity, the pre-stretching pulse from an Öffner stretcher is further broadened to above 200ps, which matches the amplification windows of the signal pulses in OPCPA and is suitable for use as a pump source in the OPCPA system. The bandwidth of the amplified pulse is 1.5 nm, and an output energy of 2mJ is achieved at a repetition rate of 10Hz.

Total-reflection active-mirror amplifier for high pulse energy and high average power by using a composite ceramic

A total-reflection active-mirror (TRAM) amplifier is functionally designed by using a composite ceramic for high pulse energy and high average power. A chirped-pulse regenerative amplifier with a cryogenic TRAM has been successfully demonstrated as a feasibility study. A 3.5mJ pulse energy is obtained at a repetition rate of 100Hz. The corresponding energy fluence on the TRAM is as high as 1.5J/cm2 for 0.46ns short pulses. The M2-factor is below 1.1 and no significant beam distortion is observed.

High energy and long pulse generation with high-birefringence photonic crystal fibre and laser-diode pumped regenerative amplifier

We report on the generation of a high energy and long pulse for pumping optical parametric chirped-pulse amplification (OPCPA) by a high-birefringence photonic crystal fibre (HB-PCF) and a laser-diode-pumped regenerative chirped pulse amplifier. Using the femtosecond pump pulse centred at 815 nm, a 1064 nm soliton pulse is produced in the HB-PCF. After injecting it into an Nd:YAG regenerative amplifier with the glass etalons, a narrow-band amplified pulse with an energy of ∼4 mJ and a duration of 235 ps is achieved at a repetition rate of 10 Hz, which is suitable for being used as a pump source in the 800 nm OPCPA system.

An amplified femtosecond laser system for material micro-/nanostructuring with an integrated Raman microscope

In order to obtain new insights into laser-induced chemical material modifications, we introduce a novel combined approach of femtosecond pulsed laser-direct writing and in situ Raman microscopy within a single experimental apparatus. A newly developed scanning microscope, the first of its kind, provides a powerful tool for micro-/nanomachining and characterization of material properties and allows us to relate materials' functionality with composition. We address the issues of light delivery to the photomodification site and show the versatility of the system using tight focusing. Amplified femtosecond pulses are generated by a Ti:sapphire laser oscillator and a chirped-pulse regenerative amplifier, both pumped by a diode-pumped frequency doubled neodymium-doped yttrium orthovanadate (Nd:YVO(4)) laser operating at 532 nm. Results of Raman spectroscopy and scanning electron microscopy images of femtosecond laser micro-/nanomachining on the surface and in the bulk of single-crystal diamond obtained from first trials of this instrument are also presented. This effective combination could help to shed light on the influence of the local structure fluctuations on controllability of the laser processing and the role of the irradiation in the ablation processes ruling out possible imprecisions coming from the use of the two independent techniques.

High-energy, diode-pumped, picosecond Yb:YAG chirped-pulse regenerative amplifier for pumping optical parametric chirped-pulse amplification

A diode-pumped, cryogenic-cooled Yb:YAG regenerative amplifier utilizing gain-narrowing has been developed. A 1.2-ns chirped-seed pulse was simultaneously amplified and compressed in the regenerative amplifier, which generated a 35-ps pulse with ~8-mJ of energy without a pulse compressor. Second-harmonics of the amplified pulse was used to pump picosecond two-color optical parametric amplification.

Design and construction of a TW-class 12-fs Ti:Sapphire chirped-pulse amplification system

We describe a design and a construction of a TW-class 12-fs Ti:sapphire chirped-pulse amplification system. We developed a broadband pulse stretcher, a broadband gain-narrowing compensator, broadband high-energy mirrors, high-energy dichroic chirped mirrors, a dispersion compensator, and a broadband pulse compressor for /spl sim/10-fs pulse generation. Utilizing these optical devices, we demonstrated a generation of 12-fs pulses from a 10-Hz-repetition-rate Ti:sapphire chirped-pulse multipass amplifier system and a 1-kHz-repetition-rate Ti:sapphire chirped-pulse regenerative amplifier system. Optimized designs of broadband Ti:sapphire amplifiers with multilayer gain-narrowing compensators and an adaptive dispersion compensator with a spatial light modulator contribute to the shorter pulse amplification.

30-mJ, diode-pumped, chirped-pulse Yb:YLF regenerative amplifier.

A diode-pumped chirped-pulse regenerative amplifier with a cooled Yb:YLF crystal has been developed. The output pulse energy is 30 mJ at 20-Hz repetition rate. A high effective extraction efficiency of 68% is obtained, which is attributed to reduced saturation fluence at low temperature and to a high effective pulse energy fluence during regenerative amplification. After pulse compression by use of a parallel grating pair, 18-mJ pulse energy and 795-fs pulse duration are obtained.